1. Field of the Invention
This invention relates to water-soluble mixtures of fatty acid ammonium salts and polyol fatty acids or alkali or ammonium salts thereof, to a process for their preparation, and to their use as corrosion inhibitors in aqueous systems.
2. Statement of Related Art
Corrosion problems repeatedly arise in industrial processes for machining metal surfaces, for example by drilling, cutting, rolling or grinding, and for cleaning metals. In the above processes and also in industrial cleaning processes taking place in the presence of water and water-containing liquid mixtures, metals susceptible to corrosion, primarily iron or iron-containing alloys, come into contact with aqueous industrial cleaning preparations, cooling waters, cooling lubricants for machining metals, etc. and, under adverse conditions, are corroded. On the one hand, this shortens the life of the machinery involved; on the other hand, in processes where the metal surfaces are subsequently to be further treated and, optionally, provided with anti-corrosion coatings, elaborate intermediate treatments have to be applied to ensure that the already corroded metal surfaces are free from corrosion for the following processes.
Amine salts and alkanolamine salts of maleamic acid and derivatives thereof are known from German Application No. 11 49 843 and from European Pat. No. 0 002 780 as corrosion inhibitors for aqueous systems. Compounds such as these show good to adequate solubility in water for use in aqueous systems, depending on the substituents, and a satisfactory corrosion-inhibiting effect for practical purposes, but are attended by the disadvantage that they foam very heavily. This is observed above all when these inhibitors are added to cooling waters or to cooling lubricants. Accordingly, a foam inhibitor had to be added when using these compounds. In addition, it was found that these compounds are sometimes very sensitive to variations in water hardness.
Alkanolamine salts of alkenylsuccinic acids are known as corrosion inhibitors for aqueous systems from German Application No. 29 43 963. In addition, amine salts of C.sub.6 -C.sub.9 fatty acids are disclosed as water-soluble corrosion inhibitors in U.S. Pat. No. 3,374,171. In this invention, fatty acids, such as caproic acid, caprylic acid, heptanoic acid and pelargonic acid, are neutralized with alkanolamines and mixed with polyoxyalkylene glycols.
The neutralization product of di-n-butylamine with a 1:1-mixture of caprylic acid and capric acid shows a better corrosion-inhibiting effect than the fatty acids neutralized with alkanolamines. However, this product has the disadvantage of an extremely unpleasant odor. Accordingly, in view of the large surfaces which are treated with corrosion inhibitors of the type in question, the surrounding atmosphere is polluted by that odor to an unacceptable extent.